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Hexagonal Software Architecture for Web Applications

Testing Main Paths with System Tests

Explore how to implement system tests in Hexagonal Architecture to verify that all application layers work cohesively. Understand how real HTTP requests and output adapters are used to test main user paths, catch bugs missed by unit tests, and create clear, readable tests that mimic real user behavior for better feedback and validation.

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On top of the pyramid are system tests. A system test starts up the whole application and runs requests against its APIApplication Programming Interface, verifying that all our layers work in concert.

Send money system test

In a system test for the “Send Money” use case, we send an HTTPHypertext Transfer Protocol request to the application and validate the response as well as the new balance of the account:

Java
@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class SendMoneySystemTest {
  @Autowired
  private TestRestTemplate restTemplate;
  @Test
  @Sql("SendMoneySystemTest.sql")
  void sendMoney() {
  
    Money initialSourceBalance = sourceAccount().calculateBalance();
    Money initialTargetBalance = targetAccount().calculateBalance();
  
    ResponseEntity response = whenSendMoney(
        sourceAccountId(),
        targetAccountId(),
        transferredAmount());
  
    then(response.getStatusCode())
        .isEqualTo(HttpStatus.OK);
  
    then(sourceAccount().calculateBalance())
        .isEqualTo(initialSourceBalance.minus(transferredAmount()));
  
    then(targetAccount().calculateBalance())
        .isEqualTo(initialTargetBalance.plus(transferredAmount()));
  
  }
  private ResponseEntity whenSendMoney(
      AccountId sourceAccountId,
      AccountId targetAccountId,
      Money amount) {
    
    HttpHeaders headers = new HttpHeaders();
    headers.add("Content-Type", "application/json");
    HttpEntity<Void> request = new HttpEntity<>(null, headers);
  
    return restTemplate.exchange(
        "/accounts/sendMoney/{sourceAccountId}/{targetAccountId}/{amount}",
        HttpMethod.POST,
        request,
        Object.class,
        sourceAccountId.getValue(),
        targetAccountId.getValue(),
        amount.getAmount());
  }
    // some helper methods omitted 
}

The @SpringBootTest annotation

With @SpringBootTest, we’re telling Spring to start up the whole network of objects that makes the application. We’re also ...